Treatment of a mixture containing cellulose

ABSTRACT

The present invention relates to a method for treating a mixture containing cellulose, comprising at least one step of adding at least one agent capable of reducing carbonyl groups. The invention further relates to a specialty cellulose pulp, obtained by a method comprising said treatment. Furthermore, the invention relates to the use of the specialty cellulose pulp according to the invention or the specialty cellulose pulp obtained by a method according to the invention for the production of cellulose derivatives or materials containing cellulose molecules, including but not limited to, cellulose ethers or cellulose esters. Cellulose derivatives obtained from the specialty cellulose pulp according to the invention display increased viscosity and/or improved brightness over cellulose derivatives obtained from specialty cellulose pulp not subjected to the inventive treatment.

FIELD OF THE INVENTION

[0001] The present invention relates to a method for treating a mixturecontaining cellulose, comprising at least one step of adding at leastone agent capable of reducing carbonyl groups. The invention furtherrelates to a specialty cellulose pulp, obtained by a method comprisingsaid treatment. Furthermore, the invention relates to the use of thespecialty cellulose pulp according to the invention or the specialtycellulose pulp obtained by a method according to the invention for theproduction of cellulose derivatives or materials containing cellulosemolecules as a raw material, including but not limited to, celluloseethers or cellulose esters. Cellulose derivatives obtained from thespecialty cellulose pulp according to the invention display increasedviscosity and/or improved brightness over cellulose derivatives obtainedfrom specialty cellulose pulp not subjected to the inventive treatment.

BACKGROUND OF THE INVENTION

[0002] Although the method according to the invention can be employedfor any mixture containing cellulose, by way of example, the treatmentof mixtures containing cellulose leading to specialty cellulose pulp isused to illustrate the particular embodiments. However, this shall notbe construed to mean that the method as claimed is only applicable tospecialty cellulose pulp. For the purpose of the present invention,wherever applicable, the term “specialty cellulose pulp” is synonymousto the general term “pulp”.

[0003] Specialty cellulose pulp is used to manufacture a number ofproducts that require physical and chemical properties not provided bythe pulp used for the manufacture of standard paper, linerboard orcardboard. Specialty cellulose pulp therefore differs from the majorportion of cellulose pulp produced in the world today.

[0004] Any treatment that a mixture containing cellulose is subjectedto, in particular if it is to be used as specialty cellulose pulp, hasto be performed as to maintain the properties important to the end use,in particular the integrity of the cellulose molecules themselves. Oneof the most important steps of treatment of a mixture containingcellulose, typically obtained from pulping wood, is a step of bleaching,or, in most applications, a multi-stage bleaching process. Bleaching iscommonly achieved by treating a pulp slurry with chemicals that eitherremove colored compounds such as lignin, or alter the structure ofcolored compounds so that they are no longer colored. The extent towhich a specialty cellulose is bleached depends on the requirements forthe end-product manufactured from the specialty cellulose pulp.

[0005] The expert in the field typically understands a bleaching processas one that increases the ISO brightness of a mixture containingcellulose. Futhermore, the expert in the field typically understandsthat bleaching is achieved primarily by oxidation processes, i.e.bleaching of any mixture containing cellulose according to the prior arttypically involves the application of an oxidizing agent. Forenvironmental reasons, common elemental chlorine bleaching usingchlorine and/or hypochlorite is successively replaced by elementalchlorine free bleaching (ECF) processes, wherein chlorine dioxidereplaces chlorine and/or hypochlorite. Totally chlorine free (TCF)bleaching uses chlorine-free bleaching agents such as oxygen orperoxides. A method for the non-chlorine bleaching of cellulose pulpusing oxygen gas in sophisticated treatment stages is described in, forexample, U.S. Pat. No. 6,126,782. Other oxidizing agents are ozone orenzymes. JP-A 0 6 033 390 for example discloses a method for using ozoneto bleach pulp. A main concern is to limit the oxidizing agent exposuretime in order to limit damage to the cellulose molecules.

[0006] In summary, bleaching techniques known to the expert in the fieldtypically involve oxidizing agents. The degree of ISO brightnessachievable by these methods of bleaching is limited to the extent thatstrong oxidizing agents (or highly concentrated oxidizing agents) whichwould result in a high degree of ISO brightness also tend to damage thecellulose molecules. In particular, strong or highly concentratedoxidizing agents tend to reduce the degree of polymerization (DP) of thecellulose.

[0007] A process known as “reductive bleaching” is used commonly forbrightening virgin mechanical pulps or pulp from recycled newsprint. Inthis process, a reducing agent, typically sodium borohydride, is used togenerate sodium hydrosulfite in situ from primary chemicals, i.e. thereducing agent is not used to reduce carbonyl-groups in the pulp but togenerate a bleaching agent. This process is disclosed, e.g. on pages 502through 504 of “Pulp Bleaching; Principles and Practice”, Dence andReeve (Eds.), TAPPI Press, 1996.

[0008] The use of reducing agents is also known in the context of latestages of the treatment of cellulose pulps. For example, U.S. Pat. No.5,501,711 discloses the use of borohydrides to treat cellulose fabricthat already had been subjected to a bleaching treatment. Here, theapplication of reducing agents improves the dyeability of saidcellulosic fibers. The U.S. Pat. No. 6,217,621 relates to strippingtextile fibers, including cellulose acetates and other products obtainedfrom specialty cellulose pulp, of their dyes by using reducing agentssuch as borohydrides.

[0009] Another process involving the use of reducing agents in thecontext of the treatment of cellulose pulp is disclosed in U.S. Pat. No.5,035,772. Said process involves treating a cellulose pulp that badalready been bleached with one or more reducing agents in order toreduce carbonyl groups on the lignin contained in the cellulose pulp.The process includes adding a complexing agent together with thereducing agent and processing the mixture at a temperature not greaterthan 40° C. This treatment is followed by at least one further step:either a treatment with a chemical that will block the phenolic hydroxylgroups of the lignin and/or a treatment to convert short-wave lightquanta to long wave light quanta. The object of the process according tothe U.S. Pat. No. 5,035,772 is to prevent the yellowing with age oflignin contained in (high yield) cellulose pulps. The process is to beused with ground-wood pulp, refiner pulp, thermo-mechanical andchemical-mechanical pulp for paper manufacture. Therefore, the U.S. Pat.No. 5,035,772 does not relate at all to the treatment of specialtycellulose pulp.

[0010] Finally, the possible use of borohydrides has been discussed in“Pulp Bleaching; Principles and Practice”, Dence and Reeve (Eds.), TAPPIPress, 1996, pages 297, wherein a borohydride is mentioned as a possibleadditive to eliminate some of the loss in strength of paper induced bythe alkaline extraction.

[0011] The object of the present invention was to provide a method oftreating a mixture containing cellulose, preferably a mixture containingcellulose leading to specialty cellulose pulp, so that the degree ofbrightness or the viscosity of cellulose derivatives obtained therefrom,or both, is/are increased over the prior art. In addition, as a result,a specialty cellulose pulp as such, leading to cellulose derivativeswith increased viscosity and/or brightness was to be provided.

SUMMARY OF THE INVENTION

[0012] Surprisingly, it was found that this object could be achieved bytreating a mixture containing cellulose with at least one step of addingat least one agent capable of reducing carbonyl groups. This treatmentcan be performed at any stage of processing a mixture containingcellulose into specialty cellulose pulp once a mixture containingcellulose has been obtained from (i) chemically pulping wood(=“cooking”), (ii) chemically and mechanically pulping wood or (iii)unpulped cotton or (iv) any combination of (i) to (iii). The inventivetreatment is either the sole step of the entire process or is performedprior to bleaching and/or after bleaching or is performed as at leastone step of a multi-stage bleaching process.

[0013] The solution according to the invention is particularlysurprising since the prior art does not teach that treating a mixturecontaining cellulose, i.e. treating a pulp, leads to cellulosederivatives obtainable from the treated pulp with improved viscosityand/or brightness in comparison to a similar cellulose derivativeobtained by the same process but excluding the inventive step of addingat least on agent capable of reducing carbonyl groups.

[0014] The present invention therefore relates to a method for treatinga mixture containing cellulose, comprising at least one step of addingat least one agent capable of reducing carbonyl groups. The inventionfurther relates to a specialty cellulose pulp, obtained by a methodcomprising said treatment. Furthermore, the invention relates to the useof the specialty cellulose pulp according to the invention or thespecialty cellulose pulp obtained by a method according to the inventionfor the production of cellulose derivatives or materials containingcellulose molecules as a raw material, including but not limited to,cellulose ethers or cellulose esters. Cellulose derivatives obtainedfrom the specialty cellulose pulp according to the invention displayincreased viscosity and/or improved brightness over cellulosederivatives obtained from specialty cellulose pulp not subjected to theinventive treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In FIG. 1, the viscosity of the end product obtained from theinventive specialty cellulose pulp, CMC, (vertical axis; units: mPa s)is shown as a function of the limiting viscosity number of the specialtycellulose pulp as defined in the standard “SCAN-CM 15:99” (horizontalaxis, units: ml/g).

[0016] In FIG. 2, the brightness of CMC powder (vertical axis, units: %brightness) is shown as a function of the intrinsic brightness of thespecialty cellulose pulp from which the CMC powder has been obtained bymeans of etherification (horizontal axis; units: % brightness)

[0017]FIG. 3 shows a typical particle size distribution of a CMC powderafter grinding in the Fritsch Pulvarisette 19 knife mill as used inExamples 1, 2 and 3. The horizontal x-axis represents the particlediameter in μm. while the vertical y-axis represents the volume of thecorresponding particles in %.

DETAILED DESCRIPTION OF THE INVENTION

[0018] A “mixture containing cellulose” according to the invention isany mixture that contains the glucose polymer of cellulose. No principallimitations exist as to the state of the cellulose source, i.e. it maybe solid, liquid, a suspension, slurry, paste or powder. Furthermore, nolimits exist as to the origin of the cellulose. In a preferredembodiment, the mixture containing cellulose is derived from cottonlinters and/or wood. In a particularly preferred embodiment, the mixturecontaining cellulose is derived from wood. Other cellulose sources, inparticular annual plants and/or biomass, (micro)biologically producedand/or derived cellulose, or cellulose from all types of cell walls areincluded as well.

[0019] Furthermore, no limitations exist with respect to the degree ofpolymerization of the mixture containing cellulose, as well as of anyproduct, such as specialty cellulose pulp and/or derivatives thereof,obtained from said mixture containing cellulose.

[0020] According to the invention, the mixture containing cellulose maybe derived from raw materials that need to be pulped. In general, theterm “pulping” refers to any process that separates the cellulose fromthe at least one component that holds the cellulose together in the rawmaterial. For example, in wood, the cellulose is held together by ligninand hemicellulose in fibers. The pulping process is meant to separate,at least partly, the lignin from the carbohydrate moieties of thesefibers.

[0021] As to pulping processes, three different methods are commonlydiscerned: (i) chemical pulping (or “cooking”), (ii) mechanical (or“groundwood”) pulping and (iii) semi-chemical or chemical-mechanicalpulping. In (i), the raw material, typically wood, is cooked in a“digester” at elevated temperatures with chemicals suited to break thebonds between the cellulose molecules and the lignin. In (ii), the rawmaterial is typically pressed against a grinder which physicallyseparates the fibers. The process (iii) refers to any combination of (i)and (ii). In the context of the present invention, no principallimitations exist as to how the pulping is to be performed, so long asthe pulping results in a mixture containing cellulose that can besubjected to the treatment according to the invention.

[0022] “Pulping” may not be necessary for all raw materials. Forexample, if cotton linters are used as the mixture containing cellulose,no chemical or mechanical pulping is necessary prior to any subsequenttreatment, including the inventive treatment and/or bleaching.

[0023] A mixture containing cellulose that has been pulped as describedabove, is commonly referred to as “pulp”. In the context of the presentinvention, the term “pulp” is to be seen as more general than the term“mixture containing cellulose”, since the term “pulp” is meant to referto the mixture containing cellulose before the inventive treatment aswell as to the treated mixture, for example the specialty cellulose pulpas obtained after the inventive treatment. By contrast, the term“mixture containing cellulose” is only meant to describe the pulp beforethe treatment according to the invention.

[0024] Although the inventive method of treating a mixture containingcellulose with the objective to obtain specialty cellulose pulp can be,in principle, performed with any mixture containing cellulose, themethod according to the invention is particularly effective, andtherefore preferred, when applied to a mixture containing cellulosederived from wood. It is further preferred to pulp the wood chemicallyprior to the inventive treatment.

[0025] As far as wood as a source for the mixture containing celluloseis concerned, both hardwood and softwood tree species may be used.Examples of softwoods include but are not limited to: pines, inparticular Southern pine, White pine, Caribbean pine; Western hemlock;spruces, in particular Norway Spruce, Sitka Spruce; Douglas fir or thelike. Examples of hardwoods include, but are not limited to: gum, maple,oak, eucalyptus, poplar, beech, or aspen. Mixtures of two or more typesof soft and/or hard wood are included as well.

[0026] Prior to the at least one step of adding at least one agentcapable of reducing carbonyl groups and/or prior and/or during and/orafter any step of pulping, the mixture containing cellulose may beoptionally subjected to any type of pretreatment. Such types ofpretreatment include but are not limited to enzyme treatments,mechanical refining, addition of additives, addition of complexingagents, treatment with delignification and other catalysts, the removalof fines as well as any combination of the aforementioned steps.

[0027] After the mixture containing cellulose has been prepared and/orobtained and/or pretreated and/or treated with at least one agentcapable of reducing carbonyl groups (i.e. the inventive treatment), themixture may be subjected to a bleaching process. The term “bleaching” asused in the context of the present invention refers to any treatment ofthe mixture containing cellulose in which the degree of brightness afterthe bleaching is increased over the degree of brightness beforebleaching. The term “ISO brightness” as used in the context of thepresent invention is defined in “ISO 2470-1999—paper, boards andpulp—measurements of the diffuse blue reflectance factor (ISObrightness)” and refers to the brightness of the pulp. It is importantto discriminate this term from the term “brightness” as used in thecontext of the present invention, which refers to the brightness of theend product, i.e. the derivative of the specialty cellulose pulp. Astandard for measuring said brightness according to the invention isgiven in Example 6. In principle, bleaching can be performed with anyagent capable of achieving the above mentioned objective.

[0028] At at least one stage of the processing of the mixture containingcellulose, obtained after pulping as has been described above, at leastone agent capable of reducing carbonyl groups (=reducing agent) is addedto the mixture containing cellulose. As a reducing agent in the contextof the present invention, every compound or mixture of compounds can beused that results in at least the partial reduction of at least a partof the carbonyl groups in at least one of the components containedwithin the pulp.

[0029] Carbonyl groups form a part of the molecular structure of themain compounds in any mixture containing cellulose. As compounds are tobe named, by way of example, cellulose, hemicellulose, lignin andresins. The carbonyl groups according to the invention that are, atleast partially, reduced in the inventive step of adding a reducingagent, may either be naturally present in the raw-material structures ormay be generated during processing or both. This is particularly true ofthe mixtures containing cellulose used for the manufacture of specialtycellulose pulps derived from wood but is also the case, to a lesserextent, for pulp derived from other raw materials, such as pulp derivedfrom cotton linters.

[0030] In principle, any agent that at least partially reduces at leasta part of the carbonyl-groups present in the mixture containingcellulose can be used. Borohydrides are particularly preferred, whilewater-compatible borohydride salts are further preferred. Such saltsinclude but are not limited to sodium borohydride, potassiumborohydride, lithium borohydride, sodium cyanoborohydride, sodiumtriacetoxyborohydride, sodium trimethoxyborohydride, tetramethylammoniumborohydride, tetramethylammonium triacetoxyborohydride,tetraethylammonium borohydride, tetrabutylammonium borohydride,tetrabutylammonium cyanoborohydride, cetyltrimethylammonium borohydride,benzyltriethylammonium borohydride, Bis(triphenyl-phosphine) copper (1)borohydride, lithium aluminium hydride, dimethylamineborane (DMAB) andmixtures of at least two of these. Preferably, said reducing agents usedshould be water-soluble.

[0031] The reducing agent can be used by itself, in combination withother reducing agents and/or in combination with stabilizers such ascalcium hydroxide, magnesium bicarbonate or other mildly basic salts.Further additional substances with other purposes may be added as well.

[0032] The reducing agents and/or additional substances may be added asa solid, a powder, a dispersion, suspension, emulsion or as a solutionin a preferred embodiment, if borohydrides are used, they are used inpowder form or in the form of a standard solution, e.g. sodiumborohydride, which can be purchased as a 12 wt % solution in 40 wt %aqueous sodium hydroxide (e.g. Borol® from Rohm and Haas, Hydrafin™ fromFinnish Chemicals (Nokia) Ltd). All commercially available forms ofthese chemicals, as well as any chemical of this kind prepared in alaboratory, may be used to carry out the treatment of a mixturecontaining cellulose as disclosed here.

[0033] As has been mentioned above, the reducing agent may be added atany stage of the processing of the mixture containing cellulose. In apreferred embodiment, the reducing agent is added in at least one stepduring a multi-stage bleaching process.

[0034] In a particularly preferred embodiment, the at least one reducingagent is added, i.e. the inventive treatment is performed, at least asthe last stage or after the last stage of a multi-stage bleachingprocess.

[0035] The content of reducing agent added in at least one step may varyfrom 0.01 to 500 g, preferably from 0.1 g·mol/ton mixture containingcellulose (dry basis) to 2000 g·mol/ton mixture containing cellulose,depending on the chemical additives and the specific composition of themixture containing cellulose. In a preferred embodiment of theinvention, wherein sodium borohydride is added as the carbonyl-reducingagent and the sole purpose of the at least one step of the treatment isthe chemical reduction of carbonyl groups, the charge is between 0.3 and100 g·mol/ton mixture containing cellulose (on a dry basis).

[0036] In a further preferred embodiment, where sodium borohydride isadded as the carbonyl-reducing agent and an additional purpose of the atleast one step of the treatment is the delignification of the mixturecontaining cellulose, the charge is from 0.1 and 500 g·mol/ton mixturecontaining cellulose (on a dry basis), preferably from 0.1 to 80 gmol/ton.

[0037] In a preferred embodiment, the reducing agent is added as the atleast one agent in at least one stage of a multi-stage bleaching processand/or is added as at least one of at least two agents in at least onestages of a multi-stage bleaching process. In particular, the reducingagents can be added simultaneously during the addition of one or moreoxidizing agents, known to the expert in the field as the traditionalbleaching agents, at one or more stages during a multi-stage bleachingprocess. It is also conceivable, that adding reducing and oxidizingagents occur as alternating or subsequent steps, optionally separated bysteps of washing or otherwise treating the specialty cellulose pulp.

[0038] The reducing agent may be added together with any other agent orsubstance, so long as the at least one additional agent does not preventthe reducing agent to at least partly reduce at least a part of thecarbonyl groups. In a preferred embodiment, the pH achieved in the pulpupon adding the at least one reducing agent is below 12.

[0039] As far as the at least one oxidizing agent that may be added in amulti-stage bleaching process is concerned, any agent(s) known to theexpert in the field may be used. Examples of such oxidizing agents maybe selected from but are not limited the following group: chlorine,chlorine dioxide, hypochlorite, chlorite, oxygen, per-compounds such asperoxide, and ozone, as well as mixtures of two or more of theaforementioned substances.

[0040] Another agent that is commonly used during the bleaching processof a specialty cellulose pulp, namely sodium hydroxide, may be addedbefore and/or during and/or after any of the at least one step ofbleaching as mentioned above. The main purpose of adding sodiumhydroxide is the extraction of at least a part of the hemicelluloseportion of the pulp, as well as, to some extent, regulation of the pHvalue. The amount and/or conditions under which the sodium hydroxide isto be added are known to the expert in the art.

[0041] The aforementioned treatment of the mixture containing cellulose,can be carried out in any reaction device known to the expert in thefield in the context of pulp bleaching processes, for example in ableaching tower, so long as the device is adapted to comply with healthand safety issues related to the use of the specific reducing agent(s)and/or any other agent used. There are no limitations as to the designand/or function of the reaction device. For example, it may be a vesselor a tube, operated in batch mode or continuously.

[0042] In a preferred embodiment, said reaction device will be a steeltower of the type known to the expert for commercial-scale cellulosepulp bleaching processes. In a further preferred embodiment, the devicewill be of dimensions such that cellulose retention time under reactionconditions ranges from up to 6 hours. Preferably, the device is ofsufficient dimensions so that the reaction time ranges up to 3.5 hours.The actual size of the reaction device is, inter alia, determined by thepulp production rate in a continuous process and, correspondingly, bythe batch volume in a batch process. Preferably, the reaction device isfitted with a fan capable of maintaining a level of hydrogen gas wellbelow the explosion limit since hydrogen gas may be generated duringtreatment with a borohydride. Any other method capable of keeping theamount of hydrogen in the reaction device below the explosion limit,such as hydrogen scavengers, controlled reactions of hydrogen or purgingthe reaction device with inert gases or mixtures containing inert gasesmay be used as well.

[0043] The mixture containing cellulose that is to be subjected to theat least one step of the treatment according to the invention is pumpedinto the aforementioned reaction device. Preferably, it is pumped in thedevice in the form of an aqueous slurry, having a content ranging from0.1 to 40 wt % of pulp based on dry mass of the mixture containingcellulose, preferably a content ranging from 1 to 25 wt %, furtherpreferred ranging from 5 to 15 wt %. The mixing of the slurry with thereducing agents may take place either inside or outside the reactiondevice, by means of a chemical mixer or any other means that produceshomogeneous mixing. Any other chemicals added to the reactor device(e.g. for pH adjustment, bleaching purposes, hemicellulose extractionpurposes or as chemical aids to the main chemical functions in theprocess stage) may also be mixed into the slurry inside or outside thereaction device. Preferably, any mixing takes place outside of thereactor device, as this facilitates the formation of an homogeneousreaction slurry.

[0044] As far as the temperature at which the at least one reducingagent is added to the mixture containing cellulose, is concerned, anytemperature is conceivable at which the at least one reducing agent atleast partly reduces carbonyl groups contained in the mixture. In caseof an integrated method comprising several process stages, in particularseveral stages of bleaching, the process temperature may be chosen to besuitable for all stages. In a preferred embodiment, the temperature willbe set as to optimize the integrated process, or, if necessary,regulated as to optimize each stage individually. In a further preferredembodiment, the multistage bleaching process is carried out at atemperature ranging from ambient temperature to 140° C.

[0045] In a further preferred embodiment and in particular if thechemical reduction of carbonyl groups in the pulp is the primary object,the temperature for the bleaching process ranges from ambienttemperature to 80° C., further preferred from 35° C. to 75° C. and yetfurther preferred from 50° C. to 60° C. Furthermore, if the function ofthe inventive treatment also relates to delignification or to any formof bleaching, in addition to chemical reduction of carbonyl groups, thetemperature of the reaction device is set to a value that allows thebest combination of bleaching action and chemical reduction of carbonylgroups. In a process stage of the process in which common bleachingchemicals known to the expert in the field are used, temperatures shouldpreferably range from ambient temperature to 80° C., further preferredfrom 30° C. to 70° C.

[0046] The heating of the reactor device is effected using heaters orheat-exchangers of the type known to the expert in the field.

[0047] The pH-value of the pulp slurry containing the previouslydescribed active chemical agents should be between 7 and 14. As for thecase of temperature, the pH of a preferred embodiment of the inventiondepends on the full process function of the process stage in question.

[0048] Most preferably, especially if sodium borohydride is used as thecarbonyl-reducing chemical, the pH should be maintained between 8 and14, in a preferred embodiment between 10 and 13 as to minimizedecomposition of the borohydride moiety and subsequent hydrogen gasrelease. A pH between 11 and 12 is particularly preferred. For the samereason, it is preferable to adjust the pH of the pulp slurry to asufficiently high pH prior to the addition of sodium borohydride. Thiscan be achieved by adding sodium hydroxide to the slurry at a pointbetween the previous process stage and the addition of sodiumborohydride. The amount of sodium hydroxide added depends on the pH ofthe mixture containing cellulose that is fed from the previous processstage.

[0049] Should the process stage where the invention is applied have theadditional function of delignification or other bleaching action usingcommon bleaching chemicals, the pH of the slurry in the reactor deviceshould preferably be set at a value from pH 8 to 14, wherein thespecific value chosen should best suit the optimal combination ofbleaching and chemical reduction of carbonyl groups in the pulp.

[0050] As a result of the treatment of the mixture containing cellulosedescribed above, in particular after treating said mixture in ableaching process comprising at least one stage of adding a reducingagent, a treated mixture containing cellulose is obtained. In thecontext of the present invention, this mixture is referred to as(treated) “specialty cellulose pulp”, i.e. as a pulp that has beentreated and can now be further processed to obtain specialty celluloseproducts. By way of example, one class of products obtainable fromspecialty cellulose pulp are cellulose ethers.

[0051] Said cellulose ethers, for example sodium carboxymethylcellulose,methylcellulose, methylhydroxyethylcellulose,methylhydroxypropylcellulose, hydroxyethylcellulose,hydroxypropylcellulose, ethylcellulose, and mixtures of at least twocomponents thereof, are used as additives in a large range of householdand industrial products. The main purpose of adding said celluloseethers to other materials lies in the possibility of controlling therheological properties of said materials. The viscosity of the celluloseether solution (henceforth termed cellulose ether viscosity), which isstrongly related to the degree of polymerisation (DP) of the cellulosein the pulp feedstock, is therefore one of the most important propertiesof cellulose ethers.

[0052] The upper limit of cellulose ether viscosity that can be obtainedis per se limited by the upper limit of the cellulose DP in thespecialty cellulose pulp from which the cellulose ether is derived, aswell as by the DP of the cellulose ether molecule followingetherification.

[0053] Furthermore, in a large proportion of products containingcellulose ethers, the appearance of the product is of high importance.Value is often attached to a cellulose ether solid that is as white aspossible, and to a cellulose ether solution that is as transparent aspossible. The upper limit of brightness of cellulose ether that may beachieved is principally limited by the upper limit of the ISO brightnessof the specialty cellulose pulp from which it is derived.

[0054] The brightness achievable for commercial cellulose ether productsis also indirectly limited by the viscosity of the specialty cellulosepulp feed-stock. This is because of a tradeoff in the production ofspecialty cellulose pulp between high ISO brightness and high celluloseDP in the specialty cellulose pulp.

[0055] The specialty cellulose pulp as obtained after the inventivetreatment with at least one agent capable of reducing carbonyl group andafter any other optional treatment, in particular after bleaching in amulti-stage bleaching process, can now be subjected to any step ofpost-treatment.

[0056] Of particular importance in this context is the removal of waterfrom the specialty cellulose pulp. This can be achieved by filtering,pressing, drying at temperatures above room temperature, applying apressure that is below the partial pressure of water etc. Examples ofother post-bleaching steps, that may be applied either prior to, during,or after water removal, are, but are not limited to, removal of fines,enzyme treatments, and the addition of or treatments with chemicalagents to improve pulp processability characteristics. In a preferredembodiment, the specialty cellulose is present in the form of a solidsheet or powder, preferably obtained after at least one step ofpost-treatment.

[0057] The specialty cellulose pulp obtained as described above can besubjected to any step of further processing and/or derivatization. Ofparticular interest in the context of the present invention is anyprocess of forming cellulose derivatives. Cellulose ethers and/orcellulose esters are of particular importance in this context. Followingbleaching and post-treatment (including a possible stage of drying), thespecialty cellulose sheets are packed in a roll or sheets of a givenconfiguration determined by the cellulose derivative producer andtransported to the cellulose derivative producer. There, the sheets aretypically cut up or ground to a powder. In the case of cellulose ethers,the pulp pieces or powder is typically pre-treated with sodium hydroxideat below room temperature and reacted with the desired etherifyingagents in an oxygen-free environment at temperatures between 60 and 100°C. The cellulose ether product is washed free of salts, dried and oftenground to become the final product.

[0058] The viscosity of a cellulose ether as obtained from the specialtycellulose pulp as described above can be improved by at least 8-50%using the treatment as disclosed in this invention compared to the sameproduct not subjected to the at least one step of adding of at least onereducing agent during the processing of the specialty cellulose pulp.Characteristic advantages of the method according to the invention overthe prior art for etherification products obtained from the specialtycellulose pulp (in a substantially oxygen-free environment) areillustrated in FIG. 1 and FIG. 2.

[0059] In FIG. 1, the effect of the method according to the invention asapplied to a mixture containing cellulose from wood pulp is shown. Theviscosity of a sodium carboxymethyl cellulose (CMC), i.e. a cellulosederivative obtained via etherification from the specialty cellulose pulpaccording to the invention, is shown in FIG. 1. Here the viscosity ofthe end product, CMC, (vertical axis; units: mPa s) is shown as afunction of the limiting viscosity number of the specialty cellulosepulp as defined in the standard “SCAN-CM 15:99” horizontal axis, units:ml/g).

[0060] It can be seen that across a broad range of specialty cellulosedegree of polymerization (as represented by its limiting viscositynumber values), the corresponding viscosity of a 1% aqueous solution ofCMC varies linearly, irrespective of whether the mixture containingcellulose is treated according to the invention (open squares; solidline indicates least square fit) or if the mixture had not been treatedwith at least one reducing agent (open triangles). The data clearly showtwo distinct linear relationships for treated and untreated pulps.However, the viscosity of the CMC resulting form the treated specialtycellulose pulp is constantly about 200 mPa s higher than the viscosityof the untreated, but otherwise same, mixture. These data provide clearevidence that specialty cellulose pulp that had not been treatedaccording to the invention does not reach its fullest degree ofpolymerization (DP) during etherification, as evidenced by asignificantly lower viscosity of the end product.

[0061] The large effect of the at least partial reduction of carbonylgroups in a specialty cellulose pulp on the brightness of its celluloseether derivative was particularly unexpected. It has been found that thebrightness could be improved from 5% to 80%. This effect is shown inFIG. 2, where the brightness of CMC powder (vertical axis, units: %brightness) is shown as a function of the intrinsic ISO brightness ofthe specialty cellulose pulp from which the CMC powder has been obtainedby means of etherification (horizontal axis; units: % brightness). Itcan be clearly seen that the brightness of the treated specialtycellulose pulp (open squares) results in a brightness that is from 5 to20% higher than the corresponding brightness of the powder resultingfrom the untreated specialty cellulose pulp (open triangles).

[0062] The present invention also relates to the product of theinventive process, i.e. to a treated specialty cellulose pulp obtainableby a process comprising the treatment of a mixture containing cellulose,wherein the treatment comprises at least one step of adding at least oneagent capable of reducing carbonyl groups. In particular, an integratedprocess may be employed. This process comprises at least the followingsteps:

[0063] (I) Chemical or chemical and mechanical pulping of a raw materialcontaining cellulose resulting in a mixture (I) containing cellulose;

[0064] (II) treating an unpulped mixture containing cellulose ortreating a mixture (I) containing cellulose, wherein the treatmentcomprises at least one step of adding at least one agent capable ofreducing carbonyl groups, resulting in a treated specialty cellulosepulp (II);

[0065] (III) at least one step of post-processing of the specialtycellulose pulp (I);

[0066] wherein the steps (I) and (III) are optional.

[0067] In a preferred embodiment, step (II) is performed as part of amulti-stage bleaching process. In a further preferred embodiment, thestep (III) of post-processing comprises at least one step of removingwater and/or of drying at temperatures above room temperature.

[0068] The specialty cellulose pulp as claimed in this invention can beused for any application for which specialty cellulose pulp is bettersuited than regular pulp used for the manufacture of paper or cardboard.In particular, all applications in which cellulose molecules alone or incombination with other materials can be used, are included.

[0069] By way of example but without the intent to limit the scope ofthe invention, the following areas of use are mentioned: manufacture ofcellulose derivatives, in particular of cellulose ethers or celluloseesters; textile fibers, in particular viscose or high tenacity rayonyarn, non-woven fabrics; micro-crystalline cellulose, formulations forfood, in particular as edible diet food, pharmaceutical or cosmeticsapplications, technical filters, absorbing materials, fluff fibers,photographic papers, as an additive during plastic molding, the use ofsaid fibers in graft copolymerisation, as a component in compositematerials, applications in packaging, paints, inks, thickeners, LCDscreens, high value specialty papers, laminates, battery separators,electrical circuits and the like.

EXAMPLES

[0070] In the following, working examples are used to illustrate thepresent invention.

[0071] Theses examples, however are not meant to limit the scope of theinvention as described above.

Example 1 Production of Specialty Cellulose Pulp According to theInvention and Subsequent Carboxymethylation

[0072] Norway spruce was cooked in batch using the acid sulfite process.Once cooking was complete, the pulp had a mean kappa number (SCAN methodC 1:77) of 46. This pulp was transferred to a bleach plant typical ofthe design found in other bleach plants used in the manufacture ofspecialty and other cellulose pulps.

[0073] In this first example the pulp bleaching process consists of fourdistinct, industrial scale stages, working continuously and in series,followed in series by a one stage, industrial-scale embodiment of theinventive treatment. All these stages, with the exception of theinventive treatments, are variations on bleach treatments common in thespecialty cellulose and other cellulose pulp industries, and are wellknown to one skilled in the art.

[0074] The main treatment at each of the five stages comprising thisexample is carried out in stainless steel reactors commonly known asbleach towers, some of which are lined inside with chemically resistantmaterials, typical of those commonly used in the specialty cellulose andother cellulose pulp industries. Some additional but importantprocedures, such as washing, dilution, filtration, and chemical dosing,are carried out either prior to the pulp entering, or after the pulpleaving the towers. Details of the conditions inside each of the fivetowers and the bleaching, extraction chemical, and reducing agentdosages used in this example of the invention can be found in Table 1.TABLE 1 Details of the conditions inside the towers at each stage ofprocessing in Example 1. Treatment stage Parameter Units Level E₀ NaOHKg/ton pulp (dry) 57 Temperature ° C. 95 Residence time Minutes 132Consistency % 11.5 Borol Solution ® Kg/ton pulp (dry) 5 D₀ pH — 2Temperature ° C. 15 Residence time Minutes 43 Consistency % 3.5 ClO₂Kg/ton pulp (dry) 8.2 P₀ pH — 11 Temperature ° C. 35 Residence timeMinutes 126 Consistency % 10 H₂O₂ Kg/ton pulp (dry) 2 D₁ pH — 2.5Temperature ° C. 45 Residence time Minutes 148 Consistency % 10 ClO₂Kg/ton pulp (dry) 10 B pH — 11.6 Temperature ° C. 53 Residence timeMinutes 163 Consistency % 10 Borol Solution ® Kg/ton pulp (dry) 5

[0075] The term “consistency” as used in the context of the presentinvention refers to the dry mass of pulp in weight percent with respectto the total mass of pulp.

[0076] The first stage of this example of the invention, the stage (E₀),is an alkaline extraction. In this stage, in addition to the maincomponent NaOH, a borohydride is added in the form of Borol Solution® (a12 wt % solution of sodium borohydride in 40 wt % aqueous sodiumhydroxide purchased from Rohm and Haas). The dosage of Borol Solution®was 5 kg/ton pulp (dry basis) which amounts to 15.9 g moles of sodiumborohydride per ton dry pulp. This dosage was carried out immediatelyprior to the pulp entering the tower. Prior to the dosage of sodiumborohydride, the pulp was twice washed with deionized water, passed overa filter and press dewatered. Following pressing and prior to the sodiumborohydride dosage, 58 kg/ton pulp (dry basis) of sodium hydroxide wasdosed. Immediately prior to the pulp entering the E₀ tower, theconsistency of the pulp slurry was 11.5%. In the E₀ bleach tower, thetemperature was maintained at 95° C. The residence time of the pulpslurry at the base of the E₀ tower was 132 minutes. The alkalineextraction stage serves the purpose of hemicelluose removal and theborohydride serves as an additive to eliminate some of the loss instrength of paper induced by the alkaline extraction.

[0077] The second stage, namely the stage (D₀), is a chlorine dioxidetreatment. Prior to entering the D₀ tower, the pulp slurry was pressedand washed with deionized water, then washed a second time over afilter. Prior to the pulp entering the D₀ tower, the pH was adjusted to1.9, and 8.2 kg/ton pulp (dry basis) of chlorine dioxide was dosed.Following this chemical dosage, the consistency of the pulp slurry was3.5%. In the D₀ tower, the temperature was maintained at 15° C. Theresidence time of the pulp slurry in the D₀ tower was 43 minutes.

[0078] The third stage, namely the stage (P₀), is an oxidative bleachingstage using hydrogen peroxide. Prior to entering the P₀ tower, thepulp-slurry was washed with deionized water over a filter. The pH of thepulp slurry was then adjusted to 10.9 using sodium hydroxide, and 2.0kg/ton pulp (dry basis) hydrogen peroxide was added. The consistency ofthe pulp slurry was then 10%. In the P₀ tower, the temperature wasmaintained at 35° C. The residence time of the pulp slurry in the P₀bleach tower was 125 minutes.

[0079] The fourth stage, namely the stage (D₁), is a chlorine dioxidetreatment. Prior to entering the D₁ tower, the pulp was washed withdeionized water over a filter. The pH of the pulp slurry was thenadjusted to 2.5 using sulphur dioxide, and 10 kg/ton pulp (dry basis) ofchlorine dioxide was dosed. In the D₁ tower, the temperature wasmaintained at 45° C. The residence time of the pulp slurry in the D₁tower was 148 minutes.

[0080] The fifth stage of this example of the invention, namely thestage (B), has the sole purpose of effecting chemical reduction of thecarbonyl groups in the pulp, and is therefore the inventive borohydridetreatment. Sodium borohydride was dosed in the form of Borol Solution®.The dosage of Borol Solution® was 5 kg/ton pulp (dry basis), whichamounts to 15.9 g moles of sodium borohydride per ton dry pulp. Thisdosage was carried out immediately prior to the pulp entering the Btower. Prior to the dosage of sodium borohydride, the pulp was washedwith deionized water over a filter and the pH of the slurry adjusted to11.5 using sodium hydroxide. Immediately prior to the slurry enteringthe B tower, its consistency was 10%. In the B tower, the temperaturewas maintained at 55° C. The residence time of the pulp slurry in the Btower was 163 minutes.

[0081] After leaving the B tower, the pulp slurry was washed withdeionized water over a filter and the pH adjusted to 4. The pulp wasthen transported to the drying section of the specialty cellulosemanufacturing process, where it was screened, washed in deionized water,and dried to a moisture content of 7%. The dried pulp was packed in aform (approx. 20 ton rolls) typical of finished product specialtycellulose that is ready for sale to other parties wishing to use this asraw material for a cellulose derivatization.

[0082] The properties of the finished specialty cellulose product can befound in Table 2. TABLE 2 Selected properties of specialty cellulosepulp produced according to Example 1. Brightness (ISO 2470-1999) (%)82.00 Limiting viscosity number (SCAN-CM 15:99) (ml/.g) 1532 S18(SCAN-C2:61) (alkali solubility of pulp; in %) 7.02

[0083] A 50 g sample of the specialty cellulose pulp manufactured usingthe inventive treatment described above and with properties as found inTable 2 was subjected to etherification yielding sodium carboxymethylcellulose (CMC).

[0084] The aforementioned specialty cellulose pulp sample was firstground using a knife mill (Fritsch pulvarisette 19). The resultingspecialty cellulose pulp powder had a mean particle size of 200 μm asmeasured by a Coulter LS 200 particle analyzer. 35 g of powder (weighedon a dry basis) and was subsequently etherified to carboxymethylcellulose according to the carboxymethylation procedure described inExample 4. The 1 wt % solution viscosity and powder brightness of theresultant carboxymethyl cellulose product was measured. Thecorresponding values can be found in Table 3. TABLE 3 Selectedproperties of CMC made from specialty cellulose pulp produced as perExample 1. The degree of substitution of the CMC was 1.05. Viscosity of1 wt % aqueous solution (mPa s) 1840 Powder brightness (%) 71.1

[0085] Details of the procedures used for viscosity and brightnessmeasurements of CMC can be found in Example 4.

Example 2 Production of Specialty Cellulose Pulp and SubsequentCarboxymethylation Without the Inventive Treatment (Comparative Example)

[0086] In this example, exactly the same processing conditions asdescribed in Example 1 (within the repeatability limits for anindustrial scale process) were used in the stages E₀, D₀, P₀ and D₁.However, no inventive treatment stage was applied in the form of theaddition of sodium borohydride or any other agent capable of reducingcarbonyl groups at stage B. In this comparative Example 2, an oxidativebleaching stage using hydrogen peroxide (P_(I)) was directly substitutedfor the inventive stage B that had been applied in Example 1. Therefore,in this case, the pulp bleaching process consisted of five distinct,industrial scale stages, working continuously and in series. Details ofthe conditions inside each of the five towers and the bleaching andextraction chemical dosages used in this example of the invention can befound in Table 4. TABLE 4 Details of the conditions inside the towers ateach stage of processing in Example 2. Treatment stage Parameter UnitsLevel E₀ NaOH Kg/ton pulp (dry) 58 Temperature ° C. 95 Residence timeMinutes 134. Consistency % 11.5 Borol Solution ® Kg/ton pulp (dry) 5. D₀pH — 1.9 Temperature ° C. 15 Residence time Minutes 43 Consistency % 3.5ClO₂ Kg/ton pulp (dry) 8.9 P₀ pH — 11 Temperature ° C. 35 Residence timeMinutes 126 Consistency % 10 H₂O₂ Kg/ton pulp (dry) 2 D₁ pH — 2.5Temperature ° C. 45 Residence time Minutes 148 Consistency % 10 ClO₂Kg/ton pulp (dry) 10 P₁ pH — 11.6 Temperature ° C. 29 Residence timeMinutes 163 Consistency % 10 H₂O₂ Kg/ton pulp (dry) 2.5

[0087] The stage P₁, being the 5^(th) treatment stage during thebleaching of the specialty cellulose pulp in this example, was ahydrogen peroxide treatment. The chemical reactor (bleach tower) usedfor this treatment was the same tower used as stage B in Example 1.Prior to entering the P₁ tower, the pulp was washed with deionized waterover a filter and 2.5 kg/ton pulp (dry basis) was then dosedsimultaneous to the pH of the slurry being adjusted to 11.8 using sodiumhydroxide. Immediately prior to the slurry entering the P₁ tower, itsconsistency was 10%. In the P₁ tower, the temperature was maintained at29° C. The residence time of the pulp slurry in the P₁ tower was 163minutes.

[0088] The properties of the finished specialty cellulose product can befound in Table 5. TABLE 5 Selected properties of specialty cellulosepulp produced according to Example 2. Brightness (ISO 2470-1999) (%)85.80 Limiting viscosity number (SCAN-CM 15:99) (ml/g) 1574 S18(SCAN-C2:61) (alkali solubility of pulp; in %) 7.00

[0089] A 50 g sample of the specialty cellulose pulp manufactured usingthe treatment described above and with properties as found in Table 5was subjected to etherification to sodium carboxymethyl cellulose (CMC).

[0090] The aforementioned specialty cellulose pulp sample was firstground using a knife mill (Fritsch pulvarisette 19). The resultantspecialty cellulose pulp powder had a mean particle size of 200 μm asmeasured by a Coulter LS 200 particle analyzer. 35 g of powder (weighedon a dry basis) was subsequently etherified to carboxymethyl celluloseaccording to the carboxymethylation procedure described in Example 4Relevant properties of the resultant carboxymethyl cellulose productwere measured, and their values are found in Table 6. TABLE 6 Selectedpropertied of CMC made from specialty cellulose pulp pro- duced as perExample 2. The degree of substitution of the CMC was 1.05. Viscosity of1 wt % aqueous solution (mpa · s) 1530 Powder brightness (%) 70.6

[0091] A comparison of the 1 wt % solution viscosity of the CMC obtainedfrom specialty cellulose pulp obtained from Example 1 (Table 3) withthat from Example 2 (Table 6), reveals a substantially superior CMCviscosity of the CMC derived from pulp from Example 1 (20% higher). Thisis despite the limiting viscosity number of the pulp from Example 1being 42 units lower than the pulp from Example 2.

[0092] Furthermore, despite the ISO pulp brightness of the specialtycellulose pulp from Example 1 being 3 units lower than the pulp fromExample 2, the CMC powder brightness is of the same magnitude. Theseimprovements in CMC viscosity per unit pulp viscosity, and CMCbrightness per unit pulp brightness, are indicative of the effect of theinventive treatment disclosed here.

[0093] Details of the procedures used for viscosity and brightnessmeasurements of CMC can be found in Examples 5 and 6.

Example 3 Post-Bleaching Processing of Specialty Cellulose Pulp Usingthe Inventive Treatment and Subsequent Carboxymethylation

[0094] In this example, a 50 g sample of the specialty cellulose pulpmanufactured using the treatment described in Example 2 and withproperties as found in Table 4 was treated as per an embodiment of theinventive treatment.

[0095] The 50 g pulp sample was partitioned into two equal halves of 25g each. These samples were separately wet and torn into strips in 2.5 Lof deionized water. The pulp suspension was then homogenized using adesintegrator (a steel rotor blade of 6 cm diameter rotating at 600 RPMfor 30 seconds). Both pulp suspensions were transferred into the samesealable plastic container. Into the pulp suspension was added 0.233 gof Borol Solution®), amounting to 5 kg of Borol Solution®/ton pulp (drybasis), or 15.9 g moles of sodium borohydride per ton pulp (dry basis).The pH was then adjusted to 11.2 using sodium hydroxide.

[0096] The container containing the pulp suspension was sealed andshaken, and set in a water bath at a temperature of 55° C. for 180minutes. The pulp suspension was then washed twice with 51 of deionizedwater and dried to a moisture content of 7%. The limiting viscositynumber and the ISO brightness of the pulp following the inventivetreatment were found to be unchanged from those of the pulp prior toapplying the inventive treatment. The pulp properties are therefore theones found in Table 5.

[0097] This specialty cellulose pulp sample was then ground using aknife mill (Fritsch pulvarisette 19). The resultant specialty cellulosepulp powder had a mean particle size of 200 μm as measured by a CoulterLS 200 particle analyzer. 35 g of powder (weighed on a dry basis) wassubsequently etherified to carboxymethyl cellulose according to thecarboxymethylation procedure described in Example 4. Relevant propertiesof the resultant carboxymethyl cellulose product were measured, andtheir values are found in Table 7. TABLE 7 Selected propertied of CMCmade from specialty cellulose pulp pro- duced as per Example 7. Thedegree of substitution of the CMC was 1.05. Viscosity of 1 wt % aqueoussolution (mpa · s) 1870 Powder brightness (%) 75.6

[0098] A comparison of the 1 wt % solution viscosity of the CMC obtainedfrom specialty cellulose pulp obtained from Example 3 (Table 7) withthat from Example 2 (Table 6), reveals a substantially superior CMCviscosity of the CMC derived from pulp from Example 2 (22% higher). Thisis despite having the same limiting viscosity number of the pulp.

[0099] Furthermore, the CMC powder brightness of the CMC obtained fromspecialty cellulose pulp obtained from Example 3 is 5 units, or 7%,higher than the CMC from example 2. This is despite the two pulps havingthe same ISO brightness values. These improvements in CMC viscosity perunit pulp viscosity, and CMC brightness per unit pulp ISO brightness,are indicative of the effect of the inventive treatment disclosed here.

Example 4 Carboxymethylation Procedure (as Used in Examples 1 Through 3)

[0100] Chemicals: Specialty Cellulose pulp, treated as per invention(Borregaard ChemCell, Sarpsborg, Norway); iso-propanol (87 wt-% in H₂Oand 100 wt-%, ρ_(iso)=0.780 g ml⁻¹); N₂ (g); sodium hydroxide (s);sodium mono-chloroacetate, 99% pure (s); acetic acid; phenolphthalein;methanol (70 wt-%, ρ_(meth)=0.891 g ml⁻¹); silver nitrate solution (0.1M); deionized water.

[0101] Equipment: Refrigerator; analytical balance accurate to1/100^(th) of gram; Parr-reactor complete with stirring (cooled),external heating-element, internal cooling element, N₂ feed andtemperature control; knife mill (Fritsch Pulverisette 19); measuringcylinders (100 ml, 500 ml); glass beaker; plastic beakers (100 ml, 2liter); graduated pipette (2-10 ml); glass mixing rod; vacuum flask;ceramic vacuum funnel; black band filter paper; watch glass (25 cmdiameter); vacuum dryer.

[0102] The purpose of this example is to illustrate the process leadingfrom the specialty cellulose pulp according to the invention to thederivative end product, in this case an etherified derivative. However,any other derivatization would be conceivable in this context, inparticular any process of esterification.

[0103] 35 g (dry basis) of specialty cellulose pulp ground in the knifemill was introduced into the Parr-reactor. Immediately following this,precooled (5° C.) isopropanol solution (448 ml 100% iso-propanol +40.7ml deionized water) was then poured in to the reactor. The heatingjacket was fixed in place and the reactor sealed. The stirrer arm itscooler were then connected. The nitrogen gas feed was turned on and theflow-rate regulated to 100 ml/min. The cooling water feeding both thestirrer and reactor cooling coil was turned on.

[0104] Stirring was set to 250 rpm and the temperature controllerprogram (0° C. for 15 mins; 5° C. per min for 2 mins to 10° C. for 60mins; 1° C. per minute for 50 mins to 60° C. for 60 minutes; 5° C. perminute for 6 mins to 20° C. for 30 mins) was initiated.

[0105] After 15 minutes at 0° C., 22.0 g NaOH (NaOH-to-cellulose molarratio is 2.5) in 20.4 ml deionized water was introduced to the reactor.This is done rapidly to avoid oxygen entering the reactor. Immediatelyafterwards, 78 ml iso-propanol (100%) was rapidly introduced. Thestirring speed was then increased to. 500 rpm for a few seconds toattain a uniform mixture then decreased again to 250 rpm and the reactorwas left for 60 minutes at 10° C.

[0106]51.3 g sodium monochloroacetate (MCA) (MCA-to-cellulose molarratio is 2.0) was mixed with 44 ml of iso-propanol (87%) and rapidlyintroduced to the reactor. The remaining, undissolved MCA residue waswashed into the reactor with a further 44 ml of 87% iso-propanol. Thestirring speed was then set at 500 rpm for a few seconds, then set backto 250 rpm. The temperature program then ensured the reactor contentswere heated to 60° C. over 50 minutes and remained at this temperaturefor 60 minutes. The total reaction time (with MCA) was therefore 120minutes.

[0107] At the completion of 60 minutes at 6o° C., the reactor contentswere neutralised (phenolphthalein indicator) using an acetic acidsolution (5 g acetic acid in 10 ml 87% iso-propanol). The reactorcontents were vacuum-filtered and the product was first washed with 700ml of iso-propanol (87%), then four times with 700 ml of methanol (70%).After the 5^(th) and final wash, the filtrate methanol was checked forbeing chloride free using a few drops of AgNO₃. No precipitation of AgClwas observed meaning the product was sufficiently chloride free.

[0108] The washed product was dried in a vacuum drying cabinet at 60° C.over night. The product was weighed to 1/100^(th) of a gram and itsmoisture content determined. The product was then ground to a powder ofmean particle size of 119 μm and a particle size distribution as shownin Figure A1, in the knife mill.

Example 5 Procedure for Measurement of the Viscosity of a CMC Solution

[0109] 2.00 g of CMC powder (dry basis) was dissolved in 200 ml ofdeionized water using a mechanical stirrer arm rotating at 200 rpm overthe course of 1 hour at room temperature. The 1 wt % CMC solution wasthen transferred to a constant temperature water bath set at 20° C.

[0110] An Anton Paar Physica UDS 200 was used to perform the viscositymeasurement. The temperature bath on the instrument was first set to 20°C., and the spindle (MK 25/8) was mounted. The measurement program wasinitiated and 5.5 ml of 1 wt % CMC solution is placed in the receptorbelow the spindle. The spindle was set in the “measuring position” andsurplus sample was removed. Measurement was initiated and the dynamicviscosity in mPa·s was read as that reported from the machinemeasurement at a shear rate of 11.3 s⁻¹ as the spindle is on the way up.

Example 6 Procedure for Measurement of the Brightness of a CMC Powder

[0111] CMC powder was placed into a stainless steel receptor fitted witha threaded press and a glass plate that ensured a pressed, smooth powdersurface. After the CMC powder was placed on the glass plate, the presswas screwed into place, and the device was turned upside down anddisassembled. The powder then lay on the circular glass plate with thesmoothed powder surface facing upwards. The plate and powder sample wasthen placed in a Minolta CM-3630 apparatus, and the CMC powderbrightness read at a wavelength of 457 nm. Each sample was preparedtwice and the average of brightness readings is reported.

[0112] It should be noted that in order to obtain completereproducibility of this procedure, any CMC powder analyzed must have thesame or a very similar mean particle size and a particle sizedistribution as that described in FIG. 3. FIG. 3 shows a typicalparticle size distribution of a CMC powder after grinding in the FritschPulvarisette 19 knife mill as used in Examples 1, 2 and 3. Thehorizontal x-axis represents the particle diameter in μm while thevertical y-axis represents the volume of the corresponding particles in%.

We claim:
 1. A method for treating a mixture containing cellulose thathas not been pulped or that has been pulped chemically or chemically andmechanically, characterized in that the treatment comprises at least onestep of adding at least one agent capable of reducing carbonyl groups.2. A method according to claim 1, characterized in that the at least oneagent capable of reducing carbonyl groups is added during at least onestep of a multi-stage bleaching process.
 3. A method according to claim2, characterized in that the at least one agent capable of reducingcarbonyl groups is added after or as the last stage of a multi-stagebleaching process.
 4. A method according to any of the preceding claims,characterized in that the mixture containing cellulose is obtained from(i) chemically or chemically and mechanically pulping wood or isobtained from (ii) unpulped cotton linters or from any combination of(i) and (ii).
 5. A method according to any of the preceding claims,characterized in that the mixture containing cellulose is an aqueousslurry of cellulose leading to a specialty cellulose pulp.
 6. A methodaccording to claim 5, characterized in that the cellulose content in theaqueous slurry is from 1 to 40% by weight, with respect to the totalweight.
 7. A method according to any of the preceding claims,characterized in that the at least one agent capable of reducingcarbonyl groups is selected from the group of borohydrides, DMAB, LiAlHand mixtures thereof.
 8. A method according to any of the precedingclaims, characterized in that the overall content of agent capable ofreducing carbonyl groups added to the mixture containing cellulose isfrom 0.1 to 200 g·moles per ton of the dry mixture containing cellulose.9. A method according to any of the preceding claims, characterized inthat the step of adding at least one agent capable of reducing carbonylgroups is performed at temperatures from ambient temperature to 90° C.10. A method according to any of the preceding claims characterized inthat the step of adding at least one agent capable of reducing carbonylgroups is performed at a pH value from 8 to
 14. 11. An integrated methodfor producing specialty cellulose pulp comprising at least the followingsteps: (I) Chemical or chemical and mechanical pulping of a raw materialcontaining cellulose resulting in a mixture (I) containing cellulose;(II) treating an unpulped mixture containing cellulose or treating amixture (I) containing cellulose wherein the treatment comprises atleast one step of adding at least one agent capable of reducing carbonylgroups, resulting in a treated specialty cellulose pulp (II); (III) atleast one step of post-processing of the specialty cellulose pulp (II);wherein the steps (I) and (III) are optional.
 12. An integrated methodaccording to claim 11, characterized in that the at least one step ofpost-processing is a step of drying.
 13. Specialty cellulose pulp,obtainable by a process comprising at least one step of treating amixture containing cellulose that has not been pulped or that has beenpulped chemically or chemically and mechanically, characterized in thatthe treatment comprises at least one step of adding at least one agentcapable of reducing carbonyl.
 14. Specialty cellulose pulp according toclaim 13, characterized in that the viscosity or the brightness, orboth, of cellulose derivatives obtained from said specialty cellulosepulp are increased over the viscosity or the ISO brightness, or both,obtained from a specialty cellulose pulp that has not been treated withthe at least one step of adding at least one agent capable of reducingcarbonyl groups.
 15. Use of the specialty cellulose pulp according tothe claims 13 or 14 or of the specialty cellulose pulp producedaccording to any of the claims 1 to 10 or of the specialty pulp producedaccording to claims 11 or 12, for the production of cellulosederivatives, including cellulose ethers or cellulose esters.
 16. Use ofthe pulp according to the claims 13 or 14 or of the specialty cellulosepulp produced according to any of the claims 1 to 10 or of the specialtypulp produced according to claim 11 or 12 for the production of viscose,composite materials, micro-crystalline cellulose formulations for food,cosmetics and pharmaceutical applications, technical filters, specialphotographic paper, as an additive during plastic molding, high-tenacityrayon yarn for tires and industrial hoses, paints, printing inks, LCDscreens, high value specialty paper applications, battery separators,circuit boards and non-woven fabrics.